RE: Mini Telemaster build. Glow conversion.
Personally, I would place the main gear about 1/2" behind the CG range. If you put it in the center of the CG range, the model is going to want to stay on its tail if the tail is pushed down. putting it 1/2" aft of the CG range assures the CG stays In-front of the gear, so the nose gear stays ON the ground.
For thrust lines, i would go with what is shown on the plans, and then as you fly it, fine-tune the thrust line with some shims to adjust the thrust angle.